The objective is to identify the mechanism of uptake of 67Ga into tumors and, in particular, the role of transferrin receptor. Our goals for the coming year are: (1) To isolate and characterize the transferrin receptor of EMT-6 sarcoma. (2) To study the inter-relationship between transport of iron and gallium in terms of subcellular macromolecualr binding. (3) To begin studies directed towards understanding the biologic basis for gallium-67 concentration by tumors, and in particular the relationship between tumor-metal metabolism and growth rate.